GitHub Actions CI

GitHub Actions is the dominant CI for new projects. The official docs cover features in isolation; this skill covers how to compose them for a fast, secure, maintainable CI.

When to use

• New repo, setting up CI from scratch.
• Existing CI is slow (>5 min for a backend; >2 min for a frontend lib).
• Migrating from Travis/CircleCI/Jenkins.
• Hardening secrets after a leak / audit finding.

When NOT to use

• Self-hosted runners with strict isolation needs at scale → look at Buildkite or Argo Workflows.
• Monorepo with 50+ services and complex DAG → Bazel + Bazel-cache is faster.

The principles